Thermoplastic thin films enjoy ubiquitous use in modern society. The most common types of such thin films are flexible, having polyolefin polymers as their chief chemical constituent. Typical uses of these thin films include but are in no way limited to: food wrap; drop-sheets for painting and decorating; vapour barriers for buildings and automotive applications including vehicle doors; as a substitute for canvas tarpaulins; as packaging films; and product labels. The widespread use of flexible polyolefin thin films stems not only from their relatively low material cost, but also from their relative ease of production. For polyolefin films less than 0.030" thickness, referred to in this specification and claims as "thin films", a film casting line is typically used to produce the film on a continuous basis in high volumes. Most importantly, the production processes used to produce polyolefin thin films can be carried out in a single process step, meaning that no significant processing of the film (other than cutting or sizing) is typically required after the initial film forming process in order to have a saleable end product. However, the polyolefin thin film thus produced has the same relatively low coefficient of friction (i.e., is relatively slippery) on both of its planar surfaces. Thus, in applications where it is desired to employ a polyolefin thin film having at least one planar surface with a coefficient of friction higher than that normally exhibited by such thin films, it is necessary to emboss, sandblast, laminate or otherwise treat such surfaces(s) of the film in a subsequent process step to achieve rougher surface characteristics, which subsequent treatment substantially increases the production costs of the end product. Moreover, the slipperiness of conventional polyolefin thin films causes specific application difficulties where surface adhesives are involved. For example, with polyolefin thin film vapour barriers used in automotive door applications, it is common to use conventional solvent-based rubber adhesives to adhere and seal the vapour barriers to the vehicle door frame behind the upholstery panels of the vehicle door. However, because of the slipperiness of conventional polyolefin thin films, such adhesion of the thin film fails over relatively short periods of time, with the result that polyolefin vapour barriers tend to fall away from vehicle door frames, particularly when the upholstery panels are removed to service components located within the interior of the vehicle door. It is not cost-efficient to laminate or otherwise further treat conventional polyolefin thin films used as vapour barriers in such applications so as to increase the coefficient of friction on the planar surface to which the adhesive is normally applied, with the result that relatively premature adhesive-to-vapour barrier failure remains an unsolved problem in relation to automotive vehicle doors.
Thus, there is a need for a polyolefin thin film having higher friction characteristics on at least one of its two planar surfaces than conventional polyolefin thin films. Thin films having such enhanced surface friction characteristics are hereinafter referred to in this specification and claims as "slip-resistant" films. Moreover, there is a need for polyolefin slip-resistant films that can be produced in a single process step. Ideally, such polyolefin slip-resistant films can be produced using existing thin film production equipment with a minimum of modification to such equipment.
Scrap tires from automotive vehicles pose a particularly serious threat to the environment. Numerous products have been developed over the last several decades which utilize to varying degrees the vulcanized rubber from scrap tires as a component in their production, thus obviating the need to send the tires so utilized to landfill or other waste disposal sites. Despite the development of such products, there remains available in the marketplace an excess of vulcanized scrap rubber from automotive tires. Such scrap rubber is available in bulk as a commodity in the form of comminuted rubber particles, substantially free of the metal and textile components of the tires. The price of such rubber particles is relatively low when compared with the price of polymers, notably, polyethylene and polypropylene. However, vulcanized rubber is not normally compatible in mixtures with polyolefins, as entrapped air from irregular and crater-like surfaces of the comminuted rubber creates voids and inconsistent texture in the prior art. This is particularly problematic in relation to polyolefin thin films, with the result that no significant use of vulcanized scrap rubber particles has been successfully made in the field of polyolefin thin films. Thus, it would, be environmentally desirable to have available in the marketplace polyolefin thin films which utilize vulcanized scrap rubber in significant amounts as one of its constituents.
It is, therefore, an object of the present invention to provide a slip-resistant polyolefin thin film having at least one planar surface with a coefficient of friction higher than that normally exhibited by such polyolefin thin films.
It is a further object of the present invention to provide a slip-resistant polyolefin thin film as aforesaid, which thin film can be produced in a single process step using existing polyolefin thin film production equipment with a minimum of modification to such equipment.
It is a further object of the present invention to provide a flexible polyolefin thin film which makes use of scrap vulcanized rubber, such as is available from recycled automotive tires, as a major constituent of the thin film, in order to reduce the need to send such scrap rubber to landfill or other waste disposal sites.
It is yet a further object of the present invention to provide a flexible polyolefin thin film which has a reduced cost when compared with conventional thin films having slip-resistant characteristics.
It is still a further object of the present invention to provide a flexible polyolefin thin film which has better noise attenuation characteristics when compared with conventional polyolefin thin films of similar thickness. This is especially advantageous in vehicle door vapour barrier applications so as to reduce road noise in the vehicle.